A conventional air-source heat pump is illustrated in FIG. 1. The heat pump in FIG. 1 typifies a “split” system comprising an outdoor heat exchanger coil and refrigerant compressor unit and an indoor heat exchanger coil contained within the building's air handling system. This heat pump can be operated in both cooling and heating modes to transfer heat to and from an outside heat source/sink.
A heat pump unit is positioned inside a housing 100 situated on the ground surface. The unit includes compressor 102, accumulator 106, heat exchanger coil 110, fan 112, reversing valve 130, and several refrigerant lines 120 and 122. The operation and interrelationship of these components is generally well known to those skilled in the art and will not be discussed in detail, however, a general summary of the function of each of theses components will be provided.
Compressor 102 pumps a refrigerant through the heat pump circuit. In cooling mode, compressor 102 pressurizes vaporized refrigerant, heating the refrigerant to a temperature higher than the outside air (typically in the range of 120° F.-140° F.). Pressurized refrigerant vapor exits compressor 102 and enters reversing valve 130 through port 138. Reversing valve 130 directs the refrigerant through port 132, through line (not shown) and into heat exchanger coil (condenser) 110. The refrigerant vapor circulates through heat exchanger coil 110 spontaneously losing heat to the outside air while condensing to a liquid. A circulating fan 112, powered by fan motor 108, forces air across the heat exchanger coil 110 and increases the rate of heat dissipation and heat exchange. The refrigerant then leaves heat exchanger coil 110 as a liquid, still under high pressure, and enters line 122 through port 118. Line 122 carries the liquid refrigerant outside heat pump housing 100, through a wall 124, and into a building to be cooled. The liquid refrigerant is then directed to an indoor air handler unit 126.
The details of an indoor heat exchange system are well known to one of ordinary skill in the art and are not schematically shown. Typically, in the indoor heat exchange system, the pressurized liquid refrigerant passes through an expansion valve causing a large pressure drop that vaporizes the refrigerant. The pressure change and the liquid to vapor phase change cools the refrigerant to a temperature lower than the inside air (typically about 40° F.-50° F.). The cooled refrigerant gas is then directed to an indoor heat exchanger coil (evaporator) to exchange heat with the indoor air and then passes out of the building.
The refrigerant gas leaves the building through line 120 and travels back to outdoor heat pump unit 100. The refrigerant gas is then directed through port 116 and line (not shown) through reversing valve 130 and port 136 to accumulator 106. From accumulator 106, the refrigerant vapor is then directed into the compressor 102 for the same circulation.
In heating mode, reversing valve 130 is switched such that the high-pressure output of compressor 102 is directed toward the indoor heat exchange system 126. The high-pressure, high temperature refrigerant vapor passes through reversing valve 130 and port 136 to line 120. The refrigerant circulates through the indoor heat exchange system where the refrigerant condenses and gives up its latent heat to the indoor air. The liquid refrigerant then travels back to heat pump 100 through line 122.
The liquid refrigerant passes through an expansion valve (not shown) and circulates through heat exchanger coil 110 where it gains latent heat from the outside air. The refrigerant then travels through port 132 to the reversing valve 130, and to accumulator 106 through port 134. The refrigerant vapor then returns to the compressor 102 where the cycle begins anew.
Existing above ground air-source heat pumps and air conditioning units are inefficient, noisy, unsightly, and take up ground space.
During the winter heating season, air-source heat pumps are less effective when the air temperature falls below 25° F.-35° F. To handle such conditions, the heating system is often supplied with a supplemental heating system, such as electrical resistance strips, to further warm the building supply air after it leaves the indoor coil.
Also during the heating season, moisture in the air outside may freeze on the outdoor coil if its surface temperature drops below 32° F. Therefore, when outside temperatures fall below about 40° F., an air-source heat pump will periodically enter a defrost cycle, during which the reversing valve intermittently sends hot refrigerant through the outdoor coils.
Exterior geothermal heat pumps are exposed to outdoor conditions of extreme heat and cold, and thus require supplemental heat and/or high percentage solutions of antifreeze to prevent them from freezing in colder climates. This reduces overall efficiency. Interior, or in-building geothermal heat pump systems exist but they create machine noise and vibration and take up interior space.